The present invention relates to a method of extruding sleeves extruded of collagen or a collagen comprising mixture for encasing sausages, comprising the successive method steps: A) feeding a collagen fluid to an extrusion head; B) guiding the collagen fluid through the extrusion head; and C) discharging the collagen fluid from the extrusion head, wherein during processing step B) the collagen fluid is transported between two rotatable and co-operating jackets which co-operating jackets are rotated in opposite directions. The present invention also relates to an extrusion head for at least partial collagen edible sleeves for encasing sausages, comprising: a collagen fluid feed; a collagen fluid guide connecting to the collagen fluid feed having an internal and an external guide jacket; and a collagen fluid discharge connecting to the collagen fluid guide. The present invention also relates to a co-extrusion sausage line, for the extrusion of an at least partial collagen edible sleeve around an extruded food dough string as well as to a sleeve extruded of collagen or a collagen comprising mixture produced with such an extrusion method, such an extrusion head and/or such an co-extrusion sausage line.
Edible casings for sausages are either made from the sub-mucosal layer of animal intestines or are manufactured from collagen fibres using extrusion technology. The collagen used as a extrusion material in the food industry to provide an edible casing can surround various types of food material. In this context extrusion is the process of shaping a product by forcing a material through a die. The collagen used for such extrusion is normally re-generated collagen e.g. from bovine or porcine skin. The specific utilization of collagen according the present invention is as edible encasing material for sausage products, both in a pure composition of the collagen as in a composition in which the collagen is mixed with other (edible) products. Collagen has a fibrous nature and due to the extrusion of the collagen the collagens fibres in the extruded sleeves have the tendency to align in line with the axis of extrusion unless it is mixed or stirred immediately before the extrusion takes place. To produce collagen casings with defined fibre alignment different types of extruders are available which can produce a “crisscross” collagen fibre orientation in the casing using rotating forces. Modern extruders apply these forces using either one rotating jacket or independently counter-rotating jackets to influence collagen alignment.
The Dutch patent application NL 6 909 339, which is a family member of U.S. Pat. No. 3,622,353, discloses the preparation of collagen-coated sausages. During the production process the collagen is extruded in tubular form upon the foodstuff. By using a counter-rotating die friction forces are applied to the collagen fibres that are extruded which is believed to lead to the orientation of the collagen fibres in such a way that the strength of the collagen coating or casing is satisfactory in all directions. To realise the required orientation of the collagen fibres this document prescribes the rotation of the jackets of the extruder with 60 to 120 r.p.m. (rotations per minute) when using dual (counter)rotating jackets. Only when one jacket is rotated the rotation speed should be higher, 120 to 240 r.p.m. to give the same relative speed between the rotating and the non-rotating jacket.
The object of the invention is to provide a method and the equipment to improve the quality control of the properties of sleeves extruded of collagen or a collagen comprising mixture of the type as stated in the introduction.